1. Field of the Invention
The invention relates to material transfer arrangements and, more particularly, to movement of materials at excavation sites under vacuum pressure.
2. Background of the Invention
The invention generally concerns apparatus that collecting soil type material from excavations during pipe replacement or similar digging operations. In such operations, it is necessary to extract soil from a hole to obtain access to underground apparatus such as a pipe. As is well known, manual removal of such material from an excavation is both labor intensive and costly.
Devices to transfer materials between locations by collecting material in a container such as a hopper and then dumping the collected material have been used extensively. U.S. Pat. No. 1,211,310 issued Jan. 2, 1917 to L. A. Griffin, for example, discloses an excavation handler with a dump valve in which material enters a hopper under steam pressure and is dumped through a small manually operated valve in the hopper bottom.
U.S. Pat. No. 3,423,130 issued Jan. 21, 1969 to J. G. Milner employs a hopper to collect material using a self-contained vacuum source to draw the material into the hopper. The vacuum source includes a level control switch operative to remove the vacuum when the hopper is full. Upon removal of the vacuum, the hopper is vented to the atmosphere and the collected material is dumped out of the hopper through a discharge spout.
U.S. Pat. No. 1,115,194 issued Oct. 27, 1914 to W. G. Hay discloses apparatus in which material enters a container through an inlet under vacuum pressure and is collected therein. The bottom of the container is conical in shape and includes an aperture held closed by the vacuum pressure. When the weight of the collected material exceeds a predetermined value, the valve is forced open so that the collected material drops through the aperture.
U.S. Pat. No. 3,645,582 issued Feb. 29, 1992 to H. Siemetzki controls the level of material collected in a hopper by means of a solenoid valve at the hopper inlet. Upon receiving signals from sensors inside the hopper, the solenoid valve closes the inlet. In another material transfer device disclosed in U.S. Pat. No. 4,172,535 issued Oct. 30, 1979 to K. C. Smith, movement of collected material in a hopper is controlled by determining the weight of the hopper and its contents.
U.S. Pat. No. 4,270,671 issued Jun. 2, 1981 to J. B. Arnold utilizes a cylindrical hopper having an expandable bellows portion. Particulate material such a grain, sand or cement are supplied to the hopper through an upstream conduit angled so that the particulate material impinges on a sheet metal box which absorbs kinetic energy and redirects the material into the hopper.
Material removed from excavation sites generally contains compressible materials such as soil mixed with other larger objects such as rocks and debris. In using the aforementioned hopper arrangements at excavation sites to replace manual removal, soil in the collected material tends to pack on the sides. Such packing of compressible material impedes both collection and discharge of material. The hoppers in the aforementioned arrangements that employ funnel shaped bottom portions to direct material discharge through a restricted aperture in the funnel are likely to suffer from caking of collected material on the sides of the hopper and in the funnel which tends to block material dumping. Also, rocks and other debris in the collected material in the funnel interfere with closure of the discharge mechanism. In the cylindrical hopper system of aforementioned U.S. Pat. No. 4,270,671, particulate material can cake and accumulate on the kinetic energy absorption box and rocks and debris falling on the kinetic energy absorber may interfere with flow of the particulate material.